1. Field of the Invention
The invention relates to a foldable ladder with collapsible crosspieces having a 90-degree pivot in the middle, the crosspieces being mounted to the sidepieces likewise with 90-degree pivots.
2. Description of the Related Art
German Disclosure Publications 29 23 397 and 33 20 519 represent art related to the present invention.
German Disclosure Publication 29 23 397 relates to a folding ladder with two sidepieces, to each of which are hinged two crosspieces. The crosspieces consist of two parts directly hinged together. The individual swivel axes lie parallel to each other and perpendicular to the plane of the ladder, with a rigid, preferably tubular, bar connecting the hinge points of the crosspieces to each other and with a support frame placed below the lowermost crosspiece. The support legs of the support frame are longer than the crosspieces and are hinged to the sidepieces as well as to each other. The tip of the support frame is placed over the ends of the support legs and provides a bearing surface for the lower end of the rigid bar when the ladder is fully expanded. The swivel axes of the legs of the support frame at the sidepieces are placed at immovable points with respect to the sidepieces, and the swivel axis in the region of the hinging of the two support legs is movable with respect to the rigid bar. The abutment face formed by the tip of the support frame is still movable with respect to the rigid bar.
Thus, with this folding ladder of known construction, a central expanding bar has been provided which is not a push rod and is not pushed inside of the sidepiece.
German Disclosure Publication 33 20 519 discloses a folding ladder in which the crosspieces are folded in the middle and are hinged to the sidepieces. It is equipped with centrally located locking rods, which do not constitute a push rod and are not placed or pushed inside a timepiece.
It has been shown that prior art folding ladders cannot always satisfy practical needs. This applies in particular to the execution of a completely uniform double-up movement.